It has been proposed to use composite material such as fiber reinforced resin and carbon reinforced material for stator fan blades of gas turbine engines and turbo jet engines. See Japanese patent laid open publication No. 2006-307698. A blade made of such composite material has a higher mechanical strength and toughness than other more conventional metallic materials for the given weight, but is known to be more prone to chipping or cracking. In particular, when an aircraft is on the ground, sands and gravels that could be ingested into the engine may be impinged upon the leading edges of the blades of the stator fan, and this could cause damages to the blades.
As a countermeasure against such a problem, it has been practiced to attach an edge protector made of sheet metal and given with a U-shaped cross section on the leading edge of each blade. The blades of stator fans for more conventional turbo jet engines used to be given with relatively simple two dimensional configurations, but those for more recently developed engines are given with more complex three dimensional configurations for the purpose of achieving a higher engine efficiency. The edge protectors for such stator fan blades are required to be formed with corresponding three dimensional configurations. Therefore, conventional press forming processes for fabricating edge protectors of two dimensional configurations have become inadequate for fabricating edge protectors having three dimensional configurations.
The processes for fabricating such three dimensional edge protectors include machining, electroforming, hydro-forming and progressive press forming processes. However, these processes have some problems. The electroforming process enables an edge protector to be formed in a highly precise manner, but is a both a time consuming and expensive process. The hydro-forming is only suitable for forming sheet metal having a relatively large thickness, and is not suitable for forming the thin sheet metal which is typically used for edge protectors. Also, a high precision may not be achieved, and the manufacturing cost is relatively high. The progressive press forming process requires a large number of press forming steps, and is highly expensive because of a need for a large number of die assemblies. Also, this is not particularly suitable for forming a three dimensional work piece at a high precision.